Negative exponent with NumPy array operand

Which version of python are you using? Perfectly works for me in Python 2.6, 2.7 and 3.2:

>>> 3**-3 == 1.0/3**3True

and with numpy 1.6.1:

>>> import numpy as np>>> arr = np.array([1,2,3,4,5], dtype='float32')>>> arr**-3 == 1/arr**3array([ True,  True,  True,  True,  True], dtype=bool)

It may be a Python 3 thing as I'm using 3.5.1 and I believe this is the error you have...

for c in np.arange(-5, 5):    print(10 ** c)---------------------------------------------------------------------------ValueError                                Traceback (most recent call last)<ipython-input-79-7232b8da64c7> in <module>()      1 for c in np.arange(-5, 5):----> 2     print(10 ** c)ValueError: Integers to negative integer powers are not allowed.

Just change it to a float and it'll should work.

for c in np.arange(-5, 5):    print(10 ** float(c))1e-050.00010.0010.010.11.010.0100.01000.010000.0

oddly enough, it works in base python 3:

for i in range(-5, 5):    print(10 ** i)1e-050.00010.0010.010.1110100100010000

it seemed to work just fine for Python 2.7.12:

Python 2.7.12 (default, Oct 11 2016, 05:24:00) [GCC 4.2.1 Compatible Apple LLVM 8.0.0 (clang-800.0.38)] on darwinType "help", "copyright", "credits" or "license" for more information.>>> import numpy as np>>> for c in np.arange(-5, 5):...     print(10 ** c)... 1e-050.00010.0010.010.1110100100010000

Perhaps use the NumPy/SciPy built-in, power

>>> import numpy as NP>>> A = 10*NP.random.rand(12).reshape(4, 3)>>> A array([[ 5.7 ,  5.05,  7.28],        [ 3.61,  9.67,  6.27],        [ 5.29,  2.8 ,  0.58],        [ 5.94,  4.9 ,  1.68]])>>> NP.power(A, -2)  array([[ 0.03,  0.04,  0.02],         [ 0.08,  0.01,  0.03],         [ 0.04,  0.13,  2.98],         [ 0.03,  0.04,  0.35]])